I think that depends on several factors.
The location is key. If you are in an area of high average wind speed but there is low sun volume then i would think a windmill generator would be more efficient and vice versa.
The space you have to install either solar panels or windmill(s) and the direction they can face will also determine there efficiency. I mean you may have a lot of space that doesn't face the sun so solar panels would not work to there full capacity. Or the available space could be sheltered from the prevailing winds by buildings etc, again making a windmill generator almost useless.
As far as costs to maintain, i personaly would think a windmill would be cheaper as they are less complicated.
I found a guide that can help with working out suitability and costs. It also gives step by step video instruction on how to make a windmill generator and solar panels. If you chose to make them yourself then the cost to install them will be significantly lower than buying them pre made.
Anyway I hope this is of some use and you can find more info here